Conventional grass cutters are mainly configured to have only one circular saw-like rotary blade which is rotated at high speed and pressed against plants to cut the plants away. Although the grass cutters of this type have a high grass cutting efficiency, grass cutting operation involves some danger as rotary teeth of the grass cutters may break, and broken pieces may fly and hit against people.
As a solution to this problem, a two-blade grass cutter has been proposed. The two-blade grass cutter has an upper blade plate and a lower blade plate. Both the upper blade plate and the lower blade plate have a disc-like shape and have a plurality of cutting blades projecting from their outer peripheral portions. The two-blade grass cutter incorporates a deceleration mechanism used to decelerate a turning effect of a motor or an engine so as to slowly rotate the upper blade plate and the lower blade plate in directions opposite to each other. Plants are cut between the cutting edges of the upper blade plate and the lower blade plate. Since the blade plates of the two-blade grass cutter slowly rotate, there is no concern for broken pieces of the blades flying away.
Japanese Patent Laid-Open No. 11-253027 discloses a grass cutter including a deceleration mechanism using a planetary gear train. The grass cutter has a sun gear including a lower blade plate and a ring gear including an upper blade plate, with a plurality of small gears being interposed between the sun gear and the ring gear to constitute a planetary gear train. More specifically, the sun gear and the ring gear are concentrically arranged with a gap present between an external gear provided in an outer peripheral portion of the sun gear and an internal gear provided in an inner periphery of the ring gear. The small gears arranged in the gap are configured to engage with both of the sun gear and the ring gear. The grass cutter has a plurality of small gears disposed at equal intervals on a circle.
The grass cutter maintains relative positional relationship between the sun gear and the ring gear with the presence of the plurality of small gears interposed therebetween. More specifically, the grass cutter has the plurality of small gears held between the sun gear and the ring gear to secure a distance between the sun gear and the ring gear. That is, the grass cutter is configured to have the plurality of small gears around the sun gear and to have the ring gear around the plurality of small gears, so that the sun gear and the ring gear are in concentric positional relationship.